The invention relates to an arrangement for mounting swing cylinders in a boom for a rock drilling unit, comprising a frame, a boom pivotally connected about vertical and horizontal shafts, relative to the frame, a lift cylinder connected between the frame and the boom for vertical lifting and lowering of the boom, a swing cylinder connected between the frame and the boom for lateral turning of the boom relative to the frame, a support for a feed beam, connected to the other end of the boom pivotally about horizontal and vertical shafts, a tilt cylinder, connected between the support and the boom for turning the support relative to the boom about a horizontal shaft, and a transverse swing cylinder connected between the boom and the support for turning the support relative to the boom about a vertical shaft.
A problem with booms for rock drilling units is that when a feed beam is vertically turned when simultaneously being laterally deviated from its upright position to either side, the end of the boom moves so as to describe an arc. The greater the upward or downward movement of the boom, the greater the simultaneous lateral outward swing. This is caused by the articulated structures of a boom and the consequent structural geometry, the elimination of which has in practice proved impossible by mechanical means. A weakness of known solutions is also that the upward and downward swing angles of booms are not symmetrical; the downward angle is narrower than the upward angle for practical reasons. Consequently the lateral deviation in both angular positions of a boom is far too large to be handled and causes much inconvenience when the boom is used. When the boom is allowed to turn to its extreme lateral angles being in its upper angular position, the joints of the cylinders may shift to a position where the boom no longer can turn back, but is locked in place.
The object of this invention is to provide an arrangement with optimum elimination of the above problems and with as equal a lateral swing as possible in the upper and lower vertical positions of a boom. The arrangement of the invention is characterized in that a swing cylinder between a frame and a boom is coupled at an angle relative to the longitudinal axis of the boom so that the longitudinal axis of the swing cylinder has a vertical downward inclination from the frame toward the end of the boom, relative to the direction of the longitudinal axis of the boom, and that the centres of the horizontal joints, relative to the base, of the swing cylinder and the boom are essentially united with each other at the base of the boom when the boom faces straight ahead relative to the frame.
An essential idea of the invention is that the swing cylinder is coupled vertically inclined relative to the longitudinal axis of the boom so that with the swing cylinder in the horizontal plane, the boom is in the middle of its vertical swing range, whereat the upward or downward swinging of the boom from this position causes an equal deviation in both the extreme upper and lower positions to the lateral swing of the boom because of the position of the swing cylinder. Correspondingly, the transverse swing cylinder needed for turning the feed beam is coupled at an angle to the longitudinal axis of the boom, whereat the turning of both the feed beam and the boom results in equal angular changes by the action of the vertical swing angle.
It is an advantage of the invention that the changes in the direction and lateral deviations of both the boom and the feed beam, when vertically turned, are essentially the same relative to the horizontal plane both above and below, as the angles between the longitudinal axis of the boom and the swing cylinder, and correspondingly the transverse swing cylinder, compensate for the vertical deviations of the boom.
The invention will be described in greater detail below, in connection with the accompanying drawings.